Safety Check

Data reveal allergic reaction risks after COVID-19 mRNA vaccines

Image of 3 vaccine bottles & a syringe

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This article is part of Harvard Medical School’s continuing coverage of medicine, biomedical research, medical education, and policy related to the SARS-CoV-2 pandemic and the disease COVID-19.

Almost immediately after the first mRNA-based COVID-19 vaccines were authorized for emergency use and administered to individuals outside of clinical trials, reports of anaphylaxis—a life-threatening whole-body allergic reaction—raised widespread concerns among experts and the public.

Now, real world data on vaccinations among employees at Mass General Brigham provide reassurances of the rarity of such serious reactions, and the ability to recover from them.

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The findings are published in the Journal of the American Medical Association.

“The COVID-19 mRNA vaccines are the first vaccines of their kind, and they have remarkable efficacy and safety across all populations. It is critical to have accurate information on allergic reactions to these vaccines, not only for our current situation, but also because this new vaccine platform is so important for future pandemic responses,” said lead author Kimberly Blumenthal, assistant professor of medicine at Harvard Medical School and co-director of the Clinical Epidemiology Program in Massachusetts General Hospital’s Division of Rheumatology, Allergy and Immunology.

With this in mind, Blumenthal and her colleagues decided to carefully document all allergic reactions, including anaphylaxis, once they began employee vaccinations at Mass General Brigham.

The team analyzed employee surveys to estimate the incidence of allergic reactions after mRNA vaccines were administered, using multiple surveillance methods to identify the true incidence of anaphylaxis.

Among 52,805 employees who were surveyed after they received their first dose of an mRNA COVID-19 vaccine, 2 percent experienced allergic reactions, and anaphylaxis occurred at a rate of 2.47 per 10,000 individuals. The employee group included an estimated 4,000 with significant allergies to foods and medications.

“To put this in perspective, this is largely comparable to anaphylactic reactions from common antibiotics,” said Blumenthal.

The investigators noted that although the incidence of anaphylaxis was higher than that estimated by the U.S. Centers for Disease Control and Prevention, which put the rate at 0.025 to 0.11 per 10,000 vaccinations, it is still exceedingly low and should provide reassurances, especially for individuals with a history of food or drug allergies.

“The only allergy exclusion for vaccination was a prior episode of anaphylaxis to an inactive ingredient in the vaccine, called polyethylene glycol, or a cross-reactive inactive ingredient called polysorbate,” said co-senior author Paige Wickner, HMS assistant professor of medicine at Brigham and Women’s Hospital.

“Another important aspect of our study is that all of our anaphylaxis cases recovered—no one had anaphylactic shock or required a breathing tube, even temporarily,” Wickner said.

Adapted from a Mass General news release.